Magnetic sensor, magnetic encoder, and lens position detection device

ABSTRACT

A magnetic sensor includes first to fourth resistors, a power supply port, a ground port, a first output port, and a second output port. The first resistor and the second resistor are located in a first region and connected in series via a first connection point connected to the first output port. The third resistor and the fourth resistor are located in a second region and connected in series via a second connection point connected to the second output port, at least a part of the second region being located at a position different from the first region in a direction parallel to an X direction. The first and second resistors are located between the third and fourth resistors in a direction parallel to a Y direction.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic sensor, and a magneticencoder and a lens position detection device using the magnetic sensor.

2. Description of the Related Art

A magnetic encoder using a magnetic sensor is used to detect theposition of a movable object whose position changes in a predetermineddirection. The predetermined direction is a straight direction or arotational direction. The magnetic encoder used to detect the positionof the movable object is configured so that the position of a magneticfield generator, such as a magnetic scale, relative to the magneticsensor changes within a predetermined range depending on the change inthe position of the movable object.

As the position of the magnetic field generator relative to the magneticsensor changes, the strength of a component of a target magnetic field,which is generated by the magnetic field generator and applied to themagnetic sensor, in one direction changes. For example, the magneticsensor detects the strength of the component of the target magneticfield in one direction, and generates two detection signals thatcorrespond to the strength of the component in the one direction andhave respective difference phases. The magnetic encoder generates adetection value having a correspondence with the position of themagnetic field generator relative to the magnetic sensor on the basis ofthe two detection signals.

A magnetic sensor including a plurality of magnetoresistive elements isused as the magnetic sensor for the magnetic encoder. For example, WO2009/031558 and EP 2267413 A1 disclose a magnetic sensor in which aplurality of giant magnetoresistive (GMR) elements are arranged as themagnetoresistive elements in a direction of relative movement between amagnet and the magnetic sensor and a direction orthogonal to thedirection of relative movement.

In particular, in the magnetic sensor disclosed in EP 2267413 A1, theplurality of GMR elements constitute a phase-A bridge circuit and aphase-B bridge circuit. In the magnetic sensor, the plurality of GMRelements are arranged in the direction of relative movement atcenter-to-center distances of λ, λ/2, or λ/4, with the center-to-centerdistance (pitch) of the N and S poles of the magnet as λ. The phase-Abridge circuit and the phase-B bridge circuit produce output waveformsλ/2 different in phase.

By the way, magnetic encoders are known to cause distortion in thewaveforms of the detection signals of their magnetic sensor due toharmonics. If the output waveforms of the detection signals of themagnetic sensor are distorted, the position of the magnetic fieldgenerator relative to the magnetic sensor is unable to be accuratelydetected. In view of this, JP 63-225124 A discloses a magnetic sensorthat cancels harmonics by arranging a plurality of magnetoresistiveelements at predetermined distances on the basis of the NS pitch of asignal magnetic field from a magnetic medium and the orders of theharmonics.

US 2015/0253162 A1 discloses a magnetic sensor in which a plurality oftunnel magnetoresistive (TMR) elements are arranged along thelongitudinal direction of a magnetic scale at positions whereodd-ordered harmonic distortion can be cancelled, on the basis of thewavelength λ of a recording signal from the magnetic scale or a pitch Pthat is ½ of λ. This magnetic sensor includes −COS detecting sections,COS detecting sections, −SIN detecting sections, and SIN detectingsections in each of which a plurality of TMR elements are compactlyarranged and that are arranged in a width direction of the magneticscale. The −COS detecting sections and the COS detecting sections arearranged in the longitudinal direction of the magnetic scale at adistance of one pitch P. The −SIN detecting sections and the SINdetecting sections are arranged in the longitudinal direction of themagnetic scale at a distance of one pitch P. The −COS detecting sectionsand the −SIN detecting sections are arranged in the longitudinaldirection of the magnetic scale at a distance of one half of one pitch P(i.e., λ/4).

In the magnetic encoder using the magnetic sensor, the magnetic sensoris installed to face the magnetic field generator in a predeterminedorientation. In reality, however, the magnetic sensor can be skewedbecause of the installation accuracy of the magnetic sensor. A skew ofthe magnetic sensor causes a problem that the detection accuracy of theposition of the magnetic field generator relative to the magnetic sensordrops. In particular, the problem due to a skew of the magnetic sensorbecomes pronounced if a plurality of magnetoresistive elements arearranged along the longitudinal direction of the magnetic scale, likethe magnetic sensor disclosed in US 2015/0253162 A1.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetic sensor thatcan suppress the occurrence of the problem due to a skew of the magneticsensor, and a magnetic encoder and a lens position detection deviceusing the magnetic sensor.

A magnetic sensor according to the present invention detects a targetmagnetic field including a magnetic field component in a first directionparallel to an imaginary straight line. The magnetic sensor according tothe present invention includes first to fourth resistors each configuredto change in resistance with strength of the magnetic field component, apower supply port to which a voltage of predetermined magnitude isapplied, a ground port that is grounded, a first output port, and asecond output port.

The first resistor and the second resistor are located in a first regionand connected in series via a first connection point connected to thefirst output port. The third resistor and the fourth resistor arelocated in a second region and connected in series via a secondconnection point connected to the second output port, at least a part ofthe second region being located at a position different from the firstregion in the first direction. An end of the first resistor opposite tothe first connection point and an end of the third resistor opposite tothe second connection point are connected to the power supply port. Anend of the second resistor opposite to the first connection point and anend of the fourth resistor opposite to the second connection point areconnected to the ground port.

The first and second resistors are located between the third and fourthresistors in a second direction orthogonal to the first direction.

In the magnetic sensor according to the present invention, a center ofgravity of the first resistor when viewed in a third directionorthogonal to the first and second directions and a center of gravity ofthe second resistor when viewed in the third direction may be located atpositions symmetrical about the imaginary straight line. A center ofgravity of the third resistor when viewed in the third direction and acenter of gravity of the fourth resistor when viewed in the thirddirection may be located at positions symmetrical about the imaginarystraight line.

In the magnetic sensor according to the present invention, a center ofgravity of a group including the first and third resistors when viewedin the third direction orthogonal to the first and second directions anda center of gravity of a group including the second and fourth resistorswhen viewed in the third direction may be located at positionssymmetrical about the imaginary straight line.

In the magnetic sensor according to the present invention, the first tofourth resistors may each include a plurality of magnetoresistiveelements. The plurality of magnetoresistive elements each include amagnetization pinned layer having a magnetization whose direction isfixed, a free layer having a magnetization whose direction is variabledepending on the direction and the strength of the magnetic fieldcomponent, and a gap layer located between the magnetization pinnedlayer and the free layer.

If each of the first to fourth resistors includes a plurality ofmagnetoresistive elements, the direction of the magnetization of themagnetization pinned layer in each of the plurality of magnetoresistiveelements included in the first and third resistors may be a firstmagnetization direction. The direction of the magnetization of themagnetization pinned layer in each of the plurality of magnetoresistiveelements included in the second and fourth resistors may be a secondmagnetization direction opposite to the first magnetization direction.

If each of the first to fourth resistors includes a plurality ofmagnetoresistive elements, the plurality of magnetoresistive elements ofthe first resistor and the plurality of magnetoresistive elements of thesecond resistor may be located at positions symmetrical about theimaginary straight line. The plurality of magnetoresistive elements ofthe third resistor and the plurality of magnetoresistive elements of thefourth resistor may be located at positions symmetrical about theimaginary straight line.

If each of the first to fourth resistors includes a plurality ofmagnetoresistive elements, each of the plurality of magnetoresistiveelements may further include a bias magnetic field generator thatgenerates a bias magnetic field in a direction intersecting the firstdirection, the bias magnetic field being applied to the free layer.Alternatively, the free layer may have magnetic shape anisotropy with adirection of an easy axis of magnetization intersecting the firstdirection.

If each of the first to fourth resistors includes a plurality ofmagnetoresistive elements, the gap layer may be a tunnel barrier layer.

A magnetic encoder according to the present invention includes themagnetic sensor according to the present invention, and a magnetic fieldgenerator that generates the target magnetic field. The magnetic sensorand the magnetic field generator are configured so that the strength ofthe magnetic field component changes with a change in a position of themagnetic field generator relative to the magnetic sensor.

The magnetic encoder according to the present invention may furtherinclude a detection value generation circuit. In such a case, themagnetic sensor may generate a first detection signal having acorrespondence with a potential at the first output port, and generate asecond detection signal having a correspondence with a potential at thesecond output port. The detection value generation circuit may generatea detection value having a correspondence with the position of themagnetic field generator relative to the magnetic sensor on the basis ofthe first and second detection signals.

In the magnetic encoder according to the present invention, the magneticfield generator may be a magnetic scale including a plurality of pairsof N and S poles alternately arranged in a predetermined direction. Insuch a case, the first and second detection signals may each contain anideal component varying periodically to trace an ideal sinusoidal curve,and an error component corresponding to a harmonic of the idealcomponent. The first to fourth resistors may be configured so that theideal component of the first detection signal and the ideal component ofthe second detection signal have respective different phases and theerror components are reduced.

A lens position detection device according to the present invention isintended to detect a position of a lens whose position is variable. Thelens position detection device according to the present inventionincludes the magnetic sensor according to the present invention, and amagnetic field generator that generates the target magnetic field. Thelens is configured to be movable in the first direction. The magneticsensor and the magnetic field generator are configured so that thestrength of the magnetic field component changes with a change in theposition of the lens.

The lens position detection device according to the present inventionmay further include a detection value generation circuit. In such acase, the magnetic sensor may generate a first detection signal having acorrespondence with a potential at the first output port, and generate asecond detection signal having a correspondence with a potential at thesecond output port. The detection value generation circuit may generatea detection value having a correspondence with the position of the lenson the basis of the first and second detection signals.

In the lens position detection device according to the presentinvention, the magnetic field generator may be a magnetic scaleincluding a plurality of pairs of N and S poles alternately arranged ina predetermined direction. In such a case, the first and seconddetection signals may each contain an ideal component varyingperiodically to trace an ideal sinusoidal curve, and an error componentcorresponding to a harmonic of the ideal component. The first to fourthresistors may be configured so that the ideal component of the firstdetection signal and the ideal component of the second detection signalhave respective different phases and the error components are reduced.

In the magnetic sensor, the magnetic encoder, and the lens positiondetection device according to the present invention, the first andsecond resistors are located between the third and fourth resistors inthe second direction. According to the present invention, the occurrenceof the problem due to a skew of the magnetic sensor can thus besuppressed.

Other and further objects, features and advantages of the presentinvention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a magnetic encoder according to afirst embodiment of the invention.

FIG. 2 is a front view showing the magnetic encoder according to thefirst embodiment of the invention.

FIG. 3 is a plan view showing a magnetic sensor according to the firstembodiment of the invention.

FIG. 4 is a circuit diagram showing the configuration of the magneticsensor according to the first embodiment of the invention.

FIG. 5 is an explanatory diagram for describing the layout of first tofourth resistors of the first embodiment of the invention.

FIG. 6 is a plan view showing a first resistor of the first embodimentof the invention.

FIG. 7 is a perspective view showing a first example of amagnetoresistive element of the first embodiment of the invention.

FIG. 8 is a perspective view showing a second example of themagnetoresistive element of the first embodiment of the invention.

FIG. 9 is an explanatory diagram schematically showing the layout of thefirst to fourth resistors in a model of a practical example.

FIG. 10 is an explanatory diagram schematically showing the layout ofthe first to fourth resistors in a model of a first comparative example.

FIG. 11 is an explanatory diagram schematically showing the layout ofthe first to fourth resistors in a model of a second comparativeexample.

FIG. 12 is a characteristic chart showing a relationship between therotation angle of the magnetic sensor and errors determined by asimulation.

FIG. 13 is a perspective view showing a lens module including a positiondetection device according to the first embodiment of the invention.

FIG. 14 is a perspective view showing the position detection deviceaccording to the first embodiment of the invention.

FIG. 15 is a perspective view showing a first modification example of amagnetoresistive element of the first embodiment of the invention.

FIG. 16 is a plan view showing a second modification example of themagnetoresistive element of the first embodiment of the invention.

FIG. 17 is a plan view showing a third modification example of themagnetoresistive element of the first embodiment of the invention.

FIG. 18 is a plan view showing a fourth modification example of themagnetoresistive element of the first embodiment of the invention.

FIG. 19 is a plan view showing a fifth modification example of themagnetoresistive element of the first embodiment of the invention.

FIG. 20 is a plan view showing a magnetic sensor according to a secondembodiment of the invention.

FIG. 21 is a plan view showing a second resistor of the secondembodiment of the invention.

FIG. 22 is a plan view showing a magnetic sensor according to a thirdembodiment of the invention.

FIG. 23 is a circuit diagram showing the configuration of the magneticsensor according to the third embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Preferred embodiments of the present invention will now be described indetail with reference to the drawings. A schematic configuration of amagnetic encoder according to a first embodiment of the presentinvention will initially be described with reference to FIGS. 1 and 2.FIG. 1 is a perspective view showing a magnetic encoder 1. FIG. 2 is afront view showing the magnetic encoder 1. The magnetic encoder 1according to the present embodiment includes a magnetic sensor 2according to the present embodiment and a magnetic field generator 3.

The magnetic field generator 3 generates a target magnetic field MF thatis a magnetic field for the magnetic sensor 2 to detect (magnetic fieldto be detected). The target magnetic field MF includes a magnetic fieldcomponent in a direction parallel to an imaginary straight line. Themagnetic sensor 2 and the magnetic field generator 3 are configured sothat the strength of the magnetic field component changes with a changein the position of the magnetic field generator 3 relative to themagnetic sensor 2. The magnetic sensor 2 detects the target magneticfield MF including the magnetic field component, and generates at leastone detection signal corresponding to the strength of the magnetic fieldcomponent.

The magnetic field generator 3 may be a magnetic scale including aplurality of pairs of N and S poles alternately arranged in apredetermined direction. The magnetic scale may be a magnetic medium,such as a magnetic tape, that is alternately magnetized to a pluralityof pairs of N and S poles. The magnetic scale may be a plurality ofmagnets arranged along the foregoing predetermined direction. Themagnetic sensor 2 or the magnetic field generator 3 is movable within apredetermined range along the predetermined direction. As the magneticsensor 2 or the magnetic field generator 3 moves, the position of themagnetic field generator 3 relative to the magnetic sensor 2 changes.The predetermined direction may be a linear direction or a rotationaldirection.

In the present embodiment, the magnetic field generator 3 is a linearscale magnetized to a plurality of pairs of N and S poles in a lineardirection. The magnetic sensor 2 or the magnetic field generator 3 ismovable along the longitudinal direction of the magnetic field generator3. As shown in FIG. 2, the distance between two N poles adjoining in thelongitudinal direction of the magnetic field generator 3 (the same asthe distance between two S poles adjoining in the longitudinal directionof the magnetic field generator 3) will be referred to as one pitch. Thesize of one pitch will be denoted by the symbol Lp.

Now, we define λ, Y, and Z directions as shown in FIGS. 1 and 2. In thepresent embodiment, a direction parallel to the longitudinal directionof the magnetic field generator 3 will be referred to as an X direction.Two mutually orthogonal directions perpendicular to the X direction arereferred to as the Y and Z directions. In FIG. 2, the Y direction isshown as a direction from the near side to the far side of FIG. 2. Theopposite directions to the λ, Y, and Z directions will be referred to as−λ, −Y, and −Z directions, respectively.

The magnetic sensor 2 is located away from the magnetic field generator3 in the Z direction. The magnetic sensor 2 is configured to be able todetect the strength of a magnetic field component MFx of the targetmagnetic field MF at a predetermined position in a direction parallel tothe X direction. For example, the strength of the magnetic fieldcomponent MFx is expressed in positive values if the direction of themagnetic field component MFx is the X direction, and in negative valuesif the direction of the magnetic field component MFx is the −Xdirection. The strength of the magnetic field component MFx changesperiodically as the magnetic sensor 2 or the magnetic field generator 3moves along the direction parallel to the X direction. The directionparallel to the X direction corresponds to a first direction accordingto the present invention.

Next, the magnetic sensor 2 will be described in detail with referenceto FIGS. 3 and 4. FIG. 3 is a plan view showing the magnetic sensor 2.FIG. 4 is a circuit diagram showing the configuration of the magneticsensor 2. As shown in FIG. 4, the magnetic encoder 1 further includes adetection value generation circuit 4. The detection value generationcircuit 4 generates a detection value Vs having a correspondence withthe position of the magnetic field generator 3 relative to the magneticsensor 2 on the basis of the at least one detection signal correspondingto the strength of the magnetic field component MFx, generated by themagnetic sensor 2. The detection value generation circuit 4 can beimplemented by an application specific integrated circuit (ASIC) or amicrocomputer, for example.

The magnetic sensor 2 includes a first resistor R11, a second resistorR12, a third resistor R21, and a fourth resistor R22 each configured tochange in resistance with the strength of the magnetic field componentMFx. The first to fourth resistors R11, R12, R21, and R22 each include aplurality of magnetoresistive elements (hereinafter referred to as MRelements) 50.

The magnetic sensor 2 further includes a power supply port V1, a groundport G1, a first output port E1, and a second output port E2. A powersupply voltage of predetermined magnitude is applied to the power supplyport V1. The ground port G1 is connected to the ground. The first andsecond output ports E1 and E2 are connected to the detection valuegeneration circuit 4. The magnetic sensor 2 is preferably driven by aconstant voltage.

The magnetic sensor 2 generates a signal having a correspondence withthe potential at the first output E1 as a first detection signal S1, andgenerates a signal having a correspondence with the potential at thesecond output port E2 as a second detection signal S2. The detectionvalue generation circuit 4 generates the detection value Vs on the basisof the first and second detection signals S1 and S2. At least either themagnetic sensor 2 or the detection value generation circuit 4 may beconfigured to be able to correct the amplitude, phase, and offset ofeach of the first and second detection signals S1 and S2.

As shown in FIG. 4, the first resistor R11 and the second resistor R12are connected in series via a first connection point P1 connected to thefirst output port E1. The third resistor R21 and the fourth resistor R22are connected in series via a second connection point P2 connected tothe second output port E2.

In circuit configuration, the first resistor R11 is located between thepower supply port V1 and the first connection point P1. An end of thefirst resistor R11 opposite to the first connection point P1 isconnected to the power supply port V1. The phrase “in circuitconfiguration” is herein used to describe layout in a circuit diagram,not in a physical configuration. The foregoing end of the first resistorR11 is an end in the circuit diagram.

In circuit configuration, the second resistor R12 is located between theground port G1 and the first connection point P1. An end (end in thecircuit diagram) of the second resistor R12 opposite to the firstconnection point P1 is connected to the ground port G1.

In circuit configuration, the third resistor R21 is located between thepower supply port V1 and the second connection point P2. An end (end inthe circuit diagram) of the third resistor R21 opposite to the secondconnection point P2 is connected to the power supply port V1.

In circuit configuration, the fourth resistor R22 is located between theground port G1 and the second connection point P2. An end (end in thecircuit diagram) of the fourth resistor R22 opposite to the secondconnection point P2 is connected to the ground port G1.

As shown in FIG. 3, the magnetic sensor 2 further includes a substrate10, and a power supply terminal 11, a ground terminal 12, a first outputterminal 13, and a second output terminal 14 that are located on thesubstrate 10. The power supply terminal 11 constitutes the power supplyport V1. The ground terminal 12 constitutes the ground port G1. Thefirst and second output terminals 13 and 14 constitute the first andsecond output ports E1 and E2, respectively.

As shown in FIG. 3, the first and second resistors R11 and R12 arelocated in a first region R1 on the substrate 10. The third and fourthresistors R21 and R22 are located in a second region R2 on the substrate10. At least a part of the second region R2 is located at a positiondifferent from the first region R1 in the direction parallel to the Xdirection. In the example shown in FIG. 3, the second region R2 overlapsthe first region R1.

The second region R2 may be located anterior to the first region R1 inthe X direction, or anterior to the first region R1 in the −X direction.FIG. 3 shows an example where a part of the second region R2 is locatedanterior to a part of the first region R1 in the X direction. The firstand second regions R1 and R2 may be located at the same position or atdifferent positions in the Z direction.

As shown in FIG. 3, the first and second resistors R11 and R12 arelocated between the third and fourth resistors R21 and R22 in adirection parallel to the Y direction. The direction parallel to the Ydirection corresponds to a second direction according to the presentinvention.

Next, a configuration of the first to fourth resistors R11, R12, R21,and R22 will be described. Each of the first and second detectionsignals S1 and S2 contains an ideal component which varies periodicallywith a predetermined signal period in such a manner as to trace an idealsinusoidal curve (including sine and cosine waveforms). In the presentembodiment, the first to fourth resistors R11, R12, R21, and R22 areconfigured so that the ideal component of the first detection signal S1and the ideal component of the second detection signal S2 haverespective different phases. The size Lp of one pitch shown in FIG. 2corresponds to one period of the ideal components, i.e., an electricalangle of 360°.

Each of the first and second detection signals S1 and S2 contains errorcomponents corresponding to harmonics of the ideal component aside fromthe ideal component. In the present embodiment, the first to fourthresistors R11, R12, R21, and R22 are configured to reduce the errorcomponents.

The configuration of the first to fourth resistors R11, R12, R21, andR22 will be described in detail below. Initially, the configuration ofthe MR elements 50 will be described. In the present embodiment, the MRelements 50 are each a spin-valve MR element. The spin-valve MR elementincludes a magnetization pinned layer having a magnetization whosedirection is fixed, a free layer having a magnetization whose directionis variable depending on the magnetic field component MFx, and a gaplayer located between the magnetization pinned layer and the free layer.The spin-valve MR element may be a tunneling magnetoresistive (TMR)element or a giant magnetoresistive (GMR) element. In particular, in thepresent embodiment, the MR element 50 is desirably a TMR element toreduce the dimensions of the magnetic sensor 2. In the TMR element, thegap layer is a tunnel barrier layer. In the GMR element, the gap layeris a nonmagnetic conductive layer. The resistance of the spin-valve MRelement changes with the angle that the magnetization direction of thefree layer forms with respect to the magnetization direction of themagnetization pinned layer. The resistance of the spin-valve MR elementis at its minimum value when the foregoing angle is 0°, and at itsmaximum value when the foregoing angle is 180°.

In FIG. 4, the arrows shown inside the first to fourth resistors R11,R12, R21, and R22 indicate the magnetization directions of themagnetization pinned layers in the respective plurality of MR elements50 included in the resistors. The magnetization directions of themagnetization pinned layers in the respective plurality of MR elements50 included in the first and third resistors R11 and R21 are a firstmagnetization direction. The magnetization directions of themagnetization pinned layers in the respective plurality of MR elements50 included in the second and fourth resistors R12 and R22 are a secondmagnetization direction opposite to the first magnetization direction.

In particular, in the present embodiment, the first magnetizationdirection is the −X direction, and the second magnetization direction isthe X direction. In such a case, the magnetization directions of thefree layers in the respective plurality of MR elements 50 change withinthe XY plane with the strength of the magnetic field component MFx.Consequently, the potential at each of the first and second output portsE1 and E2 changes with the strength of the magnetic field component MFx.

Next, the layout of the first to fourth resistors R11, R12, R21, and R22will be described. In the following description, the layout of the firstto fourth resistors R11, R12, R21, and R22 will be described withreference to the centers of gravity of the resistors when viewed in theZ direction. The Z direction corresponds to a third direction accordingto the present invention.

FIG. 5 is an explanatory diagram for describing the layout of the firstto fourth resistors R11, R12, R21, and R22. The second resistor R12 islocated at the same position as the first resistor R11 is in the Xdirection. The second resistor R12 is also located in front of the firstresistor R11 in the −Y direction.

The third resistor R21 is located at a position Lp/4 away from the firstresistor R11 in the X direction. The third resistor R21 is also locatedanterior to the first resistor R11 in the Y direction.

The fourth resistor R22 is located at a position Lp/4 away from thesecond resistor R12 in the X direction. The fourth resistor R22 islocated at the same position as the third resistor R21 is in the Xdirection. The fourth resistor R22 is also located anterior to thesecond resistor R12 in the −Y direction.

In FIG. 5, the symbol L denotes an imaginary straight line parallel tothe X direction. The imaginary straight line L corresponds to animaginary straight line according to the present invention. Inparticular, in the present embodiment, the center of gravity C11 of thefirst resistor R11 when viewed in the Z direction and the center ofgravity C12 of the second resistor R12 when viewed in the Z directionare located at positions symmetrical about the imaginary straight lineL. The center of gravity C21 of the third resistor R21 when viewed inthe Z direction and the center of gravity C22 of the fourth resistor R22when viewed in the Z direction are located at positions symmetricalabout the imaginary straight line L.

In FIG. 5, a broken-lined region denoted by the symbol RA represents agroup including the first and third resistors R11 and R21. Abroken-lined region denoted by the symbol RB represents a groupincluding the second and fourth resistors R12 and R22. The center ofgravity C1 of the group RA when viewed in the Z direction and the centerof gravity C2 of the group RB when viewed in the Z direction are locatedat positions symmetrical about the imaginary straight line L.

Next, the layout of the plurality of MR elements 50 in each of the firstto fourth resistors R11, R12, R21, and R22 will be described. Asemployed herein, a set of one or more MR elements 50 will be referred toas an element group. The first to fourth resistors R11, R12, R21, andR22 each include a plurality of element groups. To reduce the errorcomponents, the plurality of element groups are located at predetermineddistances from each other on the basis of the size Lp of one pitch. Inthe following description, the layout of the plurality of element groupswill be described with reference to predetermined positions of theelement groups. An example of the predetermined position of an elementgroup is the center of gravity of the element group when viewed in the Zdirection.

FIG. 6 is a plan view showing the first resistor R11. As shown in FIG.6, the first resistor R11 includes eight element groups 31, 32, 33, 34,35, 36, 37, and 38. Each of the element groups 31 to 38 is divided intofour sections. Each section includes one or more MR elements 50. Inother words, each element group includes four or more MR elements 50.The plurality of MR elements 50 may be connected in series within eachelement group. In such a case, the plurality of element groups may beconnected in series. Alternatively, the plurality of MR elements 50 maybe connected in series regardless of the element groups.

In FIG. 6, the element groups 31 to 38 are located to reduce an errorcomponent corresponding to the third harmonic (third-order harmonic) ofthe ideal component, an error component corresponding to the fifthharmonic (fifth-order harmonic) of the ideal component, and an errorcomponent corresponding to the seventh harmonic (seventh-order harmonic)of the ideal component. As shown in FIG. 6, the element groups 31 to 34are arranged along the X direction. The element group 32 is located at aposition Lp/10 away from the element group 31 in the X direction. Theelement group 33 is located at a position Lp/6 away from the elementgroup 31 in the X direction. The element group 34 is located at aposition Lp/10+Lp/6 away from the element group 31 in the X direction(at a position Lp/6 away from the element group 32 in the X direction).

As shown in FIG. 6, the element groups 35 to 38 are arranged along the Xdirection, anterior to the element groups 31 to 34 in the −Y direction.The element group 35 is located at a position Lp/14 away from theelement group 31 in the X direction. The element group 36 is located ata position Lp/14+Lp/10 away from the element group 31 in the X direction(at a position Lp/14 away from the element group 32 in the X direction).The element group 37 is located at a position Lp/14+Lp/6 away from theelement group 31 in the X direction (at a position Lp/14 away from theelement group 33 in the X direction). The element group 38 is located ata position Lp/14+Lp/10+Lp/6 away from the element group 31 in the Xdirection (at a position Lp/14 away from the element group 34 in the Xdirection).

The layout of a plurality of element groups for reducing a plurality oferror components is not limited to the example shown in FIG. 6. Supposenow that n and m are integers that are greater than or equal to 1 anddifferent from each other. For example, to reduce an error componentcorresponding to a (2n+1)th-order harmonic, a first element group islocated at a position Lp/(4n+2) away from a second element group in theX direction. To further reduce an error component corresponding to a(2m+1)th-order harmonic, a third element group is located at a positionLp/(4m+2) away from the first element group in the X direction, and afourth element group is located at a position Lp/(4m+2) away from thesecond element group in the X direction. In such a manner, to reduceerror components corresponding to a plurality of harmonics, each of aplurality of element groups for reducing an error componentcorresponding to one harmonic is located at a position a predetermineddistance based on the size Lp of one pitch away from a corresponding oneof a plurality of element groups for reducing an error componentcorresponding to another harmonic in the X direction.

In the present embodiment, the configuration and layout of the pluralityof element groups in each of the second to fourth resistors R12, R21,and R22 are the same as those of the plurality of element groups in thefirst resistor R11. More specifically, the second to fourth resistorsR12, R21, and R22 each include eight element groups 31 to 38 having theconfiguration and positional relationship shown in FIG. 6. The elementgroup 31 of the second resistor R12 is located at the same position asthe element group 31 of the first resistor R11 is in the X direction.The element group 31 of the third resistor R21 is located at a positionLp/4 away from the element group 31 of the first resistor R11 in the Xdirection. The element group 31 of the fourth resistor R22 is located ata position Lp/4 away from the element group 31 of the second resistorR12 in the X direction.

The configuration of the first to fourth resistors R11, R12, R21, andR22 described above makes a phase difference of the ideal component ofthe second detection signal S2 from the ideal component of the firstdetection signal S1 an odd number of times ¼ of a predetermined signalperiod (the signal period of the ideal component), and reduces the errorcomponents of the respective first and second detection signals S1 andS2.

In the light of the production accuracy of the MR elements 50 and otherfactors, the magnetization directions of the magnetization pinnedlayers, the positions of the first to fourth resistors R11, R12, R21,and R22, and the element groups 31 to 38 may be slightly different fromthe above-described directions and positions.

Next, first and second examples of an MR element 50 will be describedwith reference to FIGS. 7 and 8. FIG. 7 is a perspective view showingthe first example of the MR element 50. In the first example, the MRelement 50 includes a layered film 50A including a magnetization pinnedlayer 51, a gap layer 52, and a free layer 53 stacked in this order inthe Z direction. The layered film 50A has a square or almost squareplanar shape when viewed in the Z direction.

The bottom surface of the layered film 50A of the MR element 50 iselectrically connected to the bottom surface of the layered film 50A ofanother MR element 50 by a not-shown lower electrode. The top surface ofthe layered film 50A of the MR element 50 is electrically connected tothe top surface of the layered film 50A of yet another MR element 50 bya not-shown upper electrode. In such a manner, the plurality of MRelements 50 are connected in series. It should be appreciated that thelayers 51 to 53 of each layered film 50A may be stacked in the reverseorder to that shown in FIG. 7.

The MR element 50 further includes a bias magnetic field generator 50Bthat generates a bias magnetic field to be applied to the free layer 53.The direction of the bias magnetic field intersects the directionparallel to the X direction. In the first embodiment, the bias magneticfield generator 50B includes two magnets 54 and 55. The magnet 54 islocated in front of the layered film 50A in the −Y direction. The magnet55 is located in front of the layered film 50A in the Y direction. Inparticular, in the first example, the layered film 50A and the magnets54 and 55 are located at positions to intersect an imaginary planeparallel to the XY plane. In FIG. 7, the arrows in the magnets 54 and 55indicate the magnetization directions of the magnets 54 and 55. In thefirst example, the direction of the bias magnetic field is the Ydirection.

FIG. 8 is a perspective view showing the second example of the MRelement 50. The second example of the MR element 50 has the sameconfiguration as that of the first example of the MR element 50 exceptthe planar shape of the layered film 50A and the positions of themagnets 54 and 55. In the second example, the magnets 54 and 55 arelocated at positions different from that of the layered film 50A in theZ direction. In particular, in the example shown in FIG. 8, the magnets54 and 55 are located anterior to the layered film 50A in the Zdirection. When viewed in the Z direction, the layered film 50A has arectangular planar shape long in the Y direction. When viewed in the Zdirection, the magnets 54 and 55 are located to overlap the layered film50A.

The direction of the bias magnetic field and the layout of the magnets54 and 55 are not limited to the examples shown in FIGS. 7 and 8. Forexample, the direction of the bias magnetic field may be a directionoblique to the Y direction. The magnets 54 and 55 may be located atrespective different positions in the direction parallel to the Xdirection. Other examples of the MR element 50 will be described belowas modification examples.

Next, a method for generating the detection value Vs of the presentembodiment will be described. For example, the detection valuegeneration circuit 4 generates the detection value Vs in the followingmanner. The detection value generation circuit 4 determines an initialdetection value in the range of 0° or more and less than 360° bycalculating the arctangent of the ratio of the second detection signalS2 to the first detection signal S1, i.e., atan (S2/S1). The initialdetection value may be the value of the arctangent itself. The initialdetection value may be a value obtained by adding a predetermined angleto the value of the arctangent.

If the foregoing value of the arctangent is 0°, the position of an Spole of the magnetic field generator 3 and the position of the elementgroup 31 in each of the first and second resistors R11 and R12 coincidein the X direction. If the foregoing value of the arctangent is 180°,the position of an N pole of the magnetic field generator 3 and theposition of the element group 31 in each of the first and secondresistors R11 and R12 coincide in the X direction. The initial detectionvalue thus has a correspondence with the position of the magnetic fieldgenerator 3 relative to the magnetic sensor 2 (hereinafter, alsoreferred to as relative position) within one pitch.

The detection value generation circuit 4 also counts the number ofrotations of the electrical angle from a reference position, with oneperiod of the initial detection value as an electrical angle of 360°.One rotation of the electrical angle corresponds to the amount ofmovement of the relative position as much as one pitch. The detectionvalue generation circuit 4 generates the detection value Vs having acorrespondence with the relative position on the basis of the initialdetection value and the number of rotations of the electrical angle.

Next, the operation and effects of the magnetic encoder 1 and themagnetic sensor 2 according to the present embodiment will be described.In the present embodiment, the first and second resistors R11 and R12are located between the third and fourth resistors R21 and R22 in thedirection parallel to the Y direction. This enables the presentembodiment to suppress the occurrence of the problem that the detectionaccuracy of the position of the magnetic field generator 3 relative tothe magnetic sensor 2 drops due to a skew of the magnetic sensor 2. Suchan effect will now be described with reference to a simulation result.

A model of a practical example and models of first and secondcomparative examples used in the simulation will initially be described.The model of the practical example is a model for the magnetic encoder 1according to the present embodiment. FIG. 9 schematically shows thelayout of the first to fourth resistors R11, R12, R21, and R22 in themodel of the practical example. The layout of the first to fourthresistors R11, R12, R21, and R22 in the model of the practical exampleis the same as described with reference to FIGS. 5 and 6.

The models of the first and second comparative examples have basicallythe same configuration as that of the model of the practical example.However, the first and second comparative examples are different fromthe practical example in the layout of the first to fourth resistorsR11, R12, R21, and R22 in the direction parallel to the Y direction.

FIG. 10 schematically shows the layout of the first to fourth resistorsR11, R12, R21, and R22 in the model of the first comparative example. Inthe first comparative example, the third resistor R21 is locatedanterior to the first resistor R11 in the −Y direction. The secondresistor R12 is located anterior to the third resistor R21 in the −Ydirection. The fourth resistor R22 is located anterior to the secondresistor R12 in the −Y direction.

FIG. 11 schematically shows the layout of the first to fourth resistorsR11, R12, R21, and R22 in the model of the second comparative example.In the second comparative example, the second resistor R12 is located infront of the first resistor R11 in the −Y direction. The third resistorR21 is located anterior to the second resistor R12 in the −Y direction.The fourth resistor R22 is located in front of the third resistor R21 inthe −Y direction.

As shown in FIGS. 10 and 11, neither of the first and second comparativeexamples satisfies the requirement that the first and second resistorsR11 and R12 be located between the third and fourth resistors R21 andR22 in the direction parallel to the Y direction.

In the simulation, the magnetic sensor 2 of each model was rotated toskew by a given angle about a rotation axis parallel to the Z direction.In such a state, the position (relative position) of the magnetic fieldgenerator 3 relative to the magnetic sensor 2 of each model was changed,and the resulting error was determined. In the simulation, the rotationangle of the magnetic sensor 2 when the longitudinal direction of eachof the first to fourth resistors R11, R12, R21, and R22 coincided withthe direction parallel to the X direction was assumed as 0°.

In the simulation, the error was determined in the following manner.Initially, the relative position was changed and the value of thearctangent of the ratio of the second detection signal S2 to the firstdetection signal S1, i.e., atan (S2/S1) was determined in the range of0° or more and less than 360°. The value of atan (S2/S1) was determinedin association with the relative position expressed by an electricalangle in the range of 0° or more and less than 360°. A differencebetween the value of atan (S2/S1) and the relative position (electricalangle) associated with the value was then determined as an error.

FIG. 12 shows a relationship between the rotation angle of the magneticsensor 2 and the error determined by the simulation. In FIG. 12, thehorizontal axis represents the rotation angle of the magnetic sensor 2,and the vertical axis the error. In FIG. 12, the reference numeral 71denotes the error of the practical example. The reference numeral 72denotes the error of the first comparative example. The referencenumeral 73 denotes the error of the second comparative example. Theerrors vary periodically as the relative position changes. FIG. 12 showsdifferences between the maximum and minimum values of the errors varyingperiodically as the errors.

The greater the error, the lower the detection accuracy of the relativeposition. The simulation result shows that the error due to a skew ofthe magnetic sensor 2 can be reduced by locating the first and secondresistors R11 and R12 between the third and fourth resistors R21 and R22in the direction parallel to the Y direction. According to the presentembodiment, the occurrence of the problem that the detection accuracy ofthe relative position drops due to a skew of the magnetic sensor 2 canthus be suppressed by locating the first to fourth resistors R11, R12,R21, and R22 as described above.

According to the present embodiment, the effect of a deviation of themagnetic sensor 2 in the direction parallel to the Y direction can alsobe reduced by locating the first to fourth resistors R11, R12, R21, andR22 as described above. For example, the magnetic sensor 2 is ideallyinstalled so that the center of the magnetic sensor 2 in the directionparallel to the Y direction coincides with that of the magnetic fieldgenerator 3 in the direction parallel to the Y direction when viewed inthe Z direction. The strength of the magnetic field component MFx peaksat the center of the magnetic field generator 3 in the directionparallel to the Y direction. If the magnetic sensor 2 is located at theforegoing ideal position, the strength of the magnetic field componentMFx therefore peaks at the center of the magnetic sensor 2 in thedirection parallel to the Y direction (between the first and secondresistors R11 and R12). If the magnetic sensor 2 deviates from the idealposition in the direction parallel to the Y direction, the strength ofthe magnetic field component MFx detected by each of the first to fourthresistors R11, R12, R21, and R22 also changes.

We now focus on the first and second resistors R11 and R12 in the modelof the second comparative example shown in FIG. 11. In the model of thesecond comparative example, if the magnetic sensor 2 deviates from theideal position in the Y direction, both the magnetic field componentsMFx detected by the first and second resistors R11 and R12 decrease instrength. As a result, either one of the resistances of the first andsecond resistors R11 and R12 increases, and the other decreases.

The resistance of the first resistor R11 will be denoted by the symbolr11, and the resistance of the second resistor R12 by the symbol r12. Inthe case of constant voltage driving, the potential at the first outputport E1 is proportional to r12/(r11+r12). If either one of r11 and r12increases and the other decreases as described above, r12 changesgreatly compared to the change of r11+r12. The potential at the firstoutput port E1 thus deviates from that when the magnetic sensor 2 islocated at the ideal position.

By contrast, according to the present embodiment, if the magnetic sensor2 deviates from the ideal position in the Y direction, the strength ofthe magnetic field component MFx detected by the first resistor R11decreases and the strength of the magnetic field component MFx detectedby the second resistor R12 increases. As a result, the resistance r11 ofthe first resistor R11 and the resistance r12 of the second resistor R12both increase or both decrease. According to the present embodiment, achange in r12/(r11+r12) can thereby be suppressed compared to the modelof the second comparative example. According to the present embodiment,a change in the first detection signal S1 when the magnetic sensor 2deviates from the ideal position in the direction parallel to the Ydirection can thus be suppressed.

The foregoing description of the first and second resistors R11 and R12also applies to the third and fourth resistors R21 and R22. According tothe present embodiment, a change in the second detection signal S2 whenthe magnetic sensor 2 deviates from the ideal position in the directionparallel to the Y direction can thus be suppressed. Consequently,according to the present embodiment, the effect of a deviation of themagnetic sensor 2 in the direction parallel to the Y direction can bereduced.

Next, features based on the layout of the first to fourth resistors R11,R12, R21, and R22 will be further described with reference to FIGS. 9 to11. In FIGS. 9 to 11, the arrow denoted by the symbol D1 represents theamount of deviation between the first resistor R11 and the thirdresistor R21 in a direction parallel to the longitudinal direction ofthe magnetic field generator 3 in each model when the magnetic fieldgenerator 3 is rotated to skew by a predetermined angle clockwise inFIGS. 9 to 11 about a rotation axis parallel to the Z direction. Thearrow denoted by the symbol D2 represents the amount of deviationbetween the second resistor R12 and the fourth resistor R22 in thedirection parallel to the longitudinal direction of the magnetic fieldgenerator 3 in each model when the magnetic field generator 3 is skewedas described above. The amount of deviation refers to, for example, adistance between the corresponding ends of the two resistors. Skewingthe magnetic field generator 3 as described above is equivalent torotating the magnetic sensor 2 to skew by the predetermined angle abouta rotation axis parallel to the Z direction.

If the longitudinal direction of the magnetic field generator 3coincides with the direction parallel to the X direction, the amounts ofdeviation D1 and D2 are ¼ of the size Lp of one pitch, i.e., Lp/4. Bycontrast, if the magnetic field generator 3 is skewed as describedabove, the amounts of deviation D1 and D2 have values different fromLp/4. In the practical example shown in FIG. 9, the amount of deviationD1 is smaller than Lp/4, and the amount of deviation D2 is greater thanLp/4. In the first comparative example shown in FIG. 10 and the secondcomparative example shown in FIG. 11, both the amounts of deviation D1and D2 are greater than Lp/4.

Although not shown in the drawings, if the magnetic field generator 3 ineach model is rotated to skew by a predetermined angle counterclockwisein FIGS. 9 to 11 about the rotation axis parallel to the Z direction,the relationship in magnitude between the amounts of deviation D1 and D2and Lp/4 is reverse to the foregoing. Locating the first and secondresistors R11 and R12 between the third and fourth resistors R21 and R22in the direction parallel to the Y direction thus corresponds to eitherone of the amounts of deviation D1 and D2 increasing and the otherdecreasing when the magnetic sensor 2 or the magnetic field generator 3is skewed.

Now, a signal corresponding to a potential difference between both endsof the first resistor R11 will be referred to as a first signal. Asignal corresponding to a potential difference between both ends of thesecond resistor R12 will be referred to as a second signal. A signalcorresponding to a potential difference between both ends of the thirdresistor R21 will be referred to as a third signal. A signalcorresponding to a potential difference between both ends of the fourthresistor R22 will be referred to as a fourth signal. A phase differencebetween the first and third signals will be referred to as a first phasedifference. A phase difference between the second and fourth signalswill be referred to as a second phase difference.

If the amount of deviation D1 is Lp/4, the first phase difference is90°. If the amount of deviation D1 is less than Lp/4, the first phasedifference is less than 90°. If the amount of deviation D1 is greaterthan Lp/4, the first phase difference is greater than 90°. Therelationship between the amount of deviation D1 and the first phasedifference also applies to that between the amount of deviation D2 andthe second phase difference. Suppose that the magnetic field generator 3in each model is rotated to skew by a predetermined angle clockwise inFIGS. 9 to 11 about the rotation axis parallel to the Z direction. Insuch a case, in the practical example shown in FIG. 9, the first phasedifference is less than 90° and the second phase difference is greaterthan 90°. In the first comparative example shown in FIG. 10 and thesecond comparative example shown in FIG. 11, both the first and secondphase differences are greater than 90°.

Suppose now that the magnetic field generator 3 in each model is rotatedto skew by a predetermined angle counterclockwise in FIGS. 9 to 11 aboutthe rotation axis parallel to the Z direction. In such a case, therelationship in magnitude between the first and second phase differencesand 90° is reverse to the foregoing. Locating the first and secondresistors R11 and R12 between the third and fourth resistors R21 and R22in the direction parallel to the Y direction thus corresponds to eitherone of the first and second phase differences being less than 90° andthe other being greater than 90° when the magnetic sensor 2 or themagnetic field generator 3 is skewed.

Next, the other effects of the present embodiment will be described bycomparison with a magnetic encoder according to a third comparativeexample. A configuration of the magnetic encoder according to the thirdcomparative example will initially be described. The magnetic encoderaccording to the third comparative example has basically the sameconfiguration as that of the magnetic encoder 1 according to the presentembodiment. However, in the third comparative example, the magnetizationdirections of the magnetization pinned layers in all the MR elements 50included in the first to fourth resistors R11, R12, R21, and R22 are thesame (for example, −X direction). Moreover, in the third comparativeexample, the second resistor R12 is located at a position Lp/2 away fromthe first resistor R11 in the X direction. The fourth resistor R22 islocated at a position Lp/2 away from the third resistor R21 in the Xdirection.

The amount of deviation between the first resistor R11 and the secondresistor R12 in the direction parallel to the longitudinal direction ofthe magnetic field generator 3 will be referred to as a first amount ofdeviation. The amount of deviation between the third resistor R21 andthe fourth resistor R22 in the direction parallel to the longitudinaldirection of the magnetic field generator 3 will be referred to as asecond amount of deviation. If the longitudinal direction of themagnetic field generator 3 coincides with the direction parallel to theX direction, both the first and second amounts of deviation are Lp/2. Ifthe magnetic field generator 3 is rotated to skew by a predeterminedangle about a rotation axis parallel to the Z direction, the first andsecond amounts of deviation are both greater than Lp/2 or both smallerthan Lp/2. In such a case, offsets occur in the first and seconddetection signals S1 and S2.

By contrast, in the present embodiment, the center of gravity C11 of thefirst resistor R11 when viewed in the Z direction and the center ofgravity C12 of the second resistor R12 when viewed in the Z directionare located at positions symmetrical about the imaginary straight lineL. The center of gravity C21 of the third resistor R21 when viewed inthe Z direction and the center of gravity C22 of the fourth resistor R22when viewed in the Z direction are located at positions symmetricalabout the imaginary straight line L. In the present embodiment, if thelongitudinal direction of the magnetic field generator 3 coincides withthe direction parallel to the X direction, both the first and secondamounts of deviation are 0. If the magnetic field generator 3 is rotatedto skew by a predetermined angle about the rotation axis parallel to theZ direction, both the first and second amounts of deviation change by anamount smaller than in the third comparative example. Consequently,according to the present embodiment, the offsets of the first and seconddetection signals S1 and S2 when the magnetic sensor 2 or the magneticfield generator 3 is skewed can be reduced, compared to the thirdcomparative example.

In the present embodiment, the magnetization directions of themagnetization pinned layers in the respective plurality of MR elements50 included in the first and third resistors R11 and R21 are the −Xdirection. The magnetization directions of the magnetization pinnedlayers in the respective plurality of MR elements 50 included in thesecond and fourth resistors R12 and R22 are the X direction. Accordingto the present embodiment, the first to fourth resistors R11, R12, R21,and R22 can thus be arranged in the foregoing positional relationship.Such a positional relationship between the centers of gravity C11, C12,C21, and C22 corresponds to two resistors whose magnetization pinnedlayers have respective different magnetization directions being locatedat positions symmetrical about the imaginary straight line L.

According to the present embodiment, the dimension of the magneticsensor 2 in the direction parallel to the X direction can be madesmaller than in the third comparative example by arranging the first tofourth resistors R11, R12, R21, and R22 in the foregoing positionalrelationship.

In the present embodiment, the center of gravity C1 of the group RAincluding the first and third resistors R11 and R21 when viewed in the Zdirection and the center of gravity C2 of the group RB including thesecond and fourth resistors R12 and R22 when viewed in the Z directionare located at positions symmetrical about the imaginary straight lineL. According to the present embodiment, the dimension of the magneticsensor 2 in the direction parallel to the X direction can thus bereduced, compared to the case where the groups RA and RB are arrangedalong the direction parallel to the X direction. The foregoingpositional relationship between the centers of gravity C1 and C2corresponds to the two resistors connected to the power supply port V1(first and third resistors R11 and R21) and the two resistors connectedto the ground port G1 (second and fourth resistors R12 and R22) beinglocated at positions symmetrical about the imaginary straight line L.

In the present embodiment, as described above, the first to fourthresistors R11, R12, R21, and R22 are configured to reduce the errorcomponents corresponding to harmonics of the ideal components. Accordingto the present embodiment, the detection accuracy of the relativeposition can thus be improved. In addition, according to the presentembodiment, the dimension of the magnetic sensor 2 in the directionparallel to the X direction can be reduced while improving the detectionaccuracy of the relative position.

By the way, in the present embodiment, the magnetic sensor 2 isdesirably driven by a constant voltage. In the case of constant voltagedriving, the potential at the first output port E1 (first detectionsignal S1) is known to be given by the resistances of the first andsecond resistors R11 and R12 and the magnitude of the voltage applied tothe power supply port V1. Similarly, in the case of constant currentdriving, the potential at the first output port E1 (first detectionsignal S1) is known to be given by the resistances of the first tofourth resistors R11, R12, R21, and R22 and the value of the current forthe constant current driving.

Suppose that a signal corresponding to a potential between both ends ofa given MR element 50 contains an ideal component varying periodicallyto trace an ideal sinusoidal curve, error components corresponding toeven-ordered harmonics of the ideal component, and error componentscorresponding to odd-ordered harmonics of the ideal component. Supposealso that the first to fourth resistors R11, R12, R21, and R22 areconfigured to reduce the error components corresponding to theodd-ordered harmonics of the first and second detection signals S1 andS2. In such a case, with the constant voltage driving, no errorcomponents corresponding to even-ordered harmonic components occur inthe first detection signal S1. By contrast, with the constant currentdriving, error components corresponding to even-ordered harmoniccomponents occur in the first detection signal S1. In the case of theconstant current driving, the first to fourth resistors R11, R12, R21,and R22 therefore need to be configured to reduce the error componentscorresponding to the even-ordered harmonic components of the firstdetection signal S1, as well as to reduce the error componentscorresponding to the odd-ordered harmonic components of the firstdetection signal S1. From such a point of view, the magnetic sensor 2 isdesirably driven by a constant voltage.

The foregoing description of the first detection signal S1 also appliesto the second detection signal S2.

Next, a lens position detection device (hereinafter, referred to simplyas a position detection device) according to the present embodiment willbe described with reference to FIGS. 13 and 14. FIG. 13 is a perspectiveview showing a lens module including the position detection deviceaccording to the present embodiment. FIG. 14 is a perspective viewshowing the position detection device according to the presentembodiment.

A lens module 300 shown in FIG. 13 constitutes a part of a smartphonecamera, for example. The lens module 300 is used in combination with animage sensor 310 using a complementary metal-oxide-silicon (CMOS) sensoror the like. In the example shown in FIG. 13, the lens module 300includes a triangular prism 302, and three lenses 303A, 303B, and 303Clocated between the image sensor 310 and the prism 302. At least one ofthe lenses 303A, 303B, and 303C is configured to be movable by anot-shown driving unit so that at least either focusing or zooming canbe performed.

FIG. 14 shows a lens 303 among the lenses 303A, 303B, and 303C. The lensmodule 300 further includes a lens holder 304 that holds the lens 303,and a shaft 305. The lens module 300 can change the position of the lens303 in an optical axis direction of the lens 303 by using the lensholder 304, the shaft 305, and the not-shown driving unit. In FIG. 14,the arrow denoted by the symbol D indicates the moving direction of thelens 303.

The lens module 300 further includes a position detection device 301 fordetecting the position of the lens 303 whose position is variable. Theposition detection device 301 is used to detect the position of the lens303 in performing focusing or zooming.

The position detection device 301 is a magnetic position detectiondevice, and includes the magnetic sensor 2 according to the presentembodiment and the magnetic field generator 3 of the present embodiment.In the lens module 300, the magnetic sensor 2 and the magnetic fieldgenerator 3 are configured so that the strength of the magnetic fieldcomponent MFx (see FIG. 2) changes as the position of the lens 303changes in the moving direction D. Specifically, the magnetic sensor 2is fixed, and the magnetic field generator 3 is configured to be movablewith the lens 303 in the moving direction D. The moving direction D isparallel to the X direction shown in FIGS. 1 and 2. When the position ofthe lens 303 changes, the position of the magnetic field generator 3relative to the magnetic sensor 2 thus changes, and as a result, thestrength of the magnetic field component MFx changes.

The position detection device 301 further includes the detection valuegeneration circuit 4 of the present embodiment (see FIG. 4). Theposition detection device 301 generates a detection value Vs having acorrespondence with the position of the lens 303 on the basis of thefirst and second detection signals 51 and S2 generated by the magneticsensor 2. The position of the lens 303 has a correspondence with theposition of the magnetic field generator 3 relative to the magneticsensor 2. The method for generating the detection value Vs by theposition detection device 301 is the same as the foregoing method forgenerating the detection value Vs.

Modification Examples

Next, first to fifth modification examples of the MR element 50 of thepresent embodiment will be described. The first modification example ofthe MR element 50 will initially be described with reference to FIG. 15.The first modification example of the MR element 50 has basically thesame configuration as that of the first example of the MR element 50shown in FIG. 7. However, in the first modification example, the layeredfilm 50A has a circular or substantially circular planar shape whenviewed in the Z direction.

Next, the second modification example of the MR element 50 will bedescribed with reference to FIG. 16. The second modification example isdifferent from the first modification example in the following points.The second modification example does not include the bias magnetic fieldgenerator 50B. In the second modification example, the planar shape ofthe layered film 50A when viewed in the Z direction is an ellipse whosemajor axis direction intersects the direction parallel to the Xdirection. The free layer 53 of the MR element 50 has magnetic shapeanisotropy with the direction of the easy axis of magnetizationintersecting the X direction. In the example shown in FIG. 16, thedirection of the easy axis of magnetization is parallel to the Ydirection. The direction of the easy axis of magnetization may beoblique to the Y direction.

Next, the third modification example of the MR element 50 will bedescribed with reference to FIG. 17. The third modification example isdifferent from the second modification example in the following points.In the third modification example, the MR element 50 includes twolayered films 50A1 and 50A2 instead of the layered film 50A according tothe second modification example. The layered films 50A1 and 50A2 eachhave the same configuration and shape as those of the layered film 50Aaccording to the second modification example. The layered films 50A1 and50A2 are connected in parallel by electrodes to constitute a layeredfilm pair. The layered film pair is connected to the layered film pairof another MR element 50 in series by an electrode. For example, thebottom surfaces of the respective layered films 50A1 and 50A2 areelectrically connected to the bottom surfaces of the respective layeredfilms 50A1 and 50A2 of another MR element 50 by a not-shown lowerelectrode. The top surfaces of the respective layered films 50A1 and50A2 are electrically connected to the top surfaces of the respectivelayered films 50A1 and 50A2 of yet another MR element 50 by a not-shownupper electrode.

Next, the fourth modification example of the MR element 50 will bedescribed with reference to FIG. 18. The fourth modification example isdifferent from the second modification example in the following points.The planar shape of the layered film 50A when viewed in the Z directionis a rectangle whose longitudinal direction intersects the directionparallel to the X direction. The free layer 53 of the MR element 50 hasmagnetic shape anisotropy with the direction of the easy axis ofmagnetization intersecting the X direction. In the example shown in FIG.18, the direction of the easy axis of magnetization is parallel to the Ydirection. The direction of the easy axis of magnetization may beoblique to the Y direction.

Next, the fifth modification example of the MR element 50 will bedescribed with reference to FIG. 19. The fifth modification example isconstituted by replacing the layered films 50A1 and 50A2 according tothe third modification example with two layered films 50A3 and 50A4having the same configuration and shape as those of the layered film 50Aaccording to the fourth modification example. The layered films 50A3 and50A4 are connected in parallel by electrodes to constitute a layeredfilm pair. The layered film pair is connected to the layered film pairof another MR element 50 in series by an electrode.

Second Embodiment

A second embodiment of the present invention will now be described withreference to FIGS. 20 and 21. FIG. 20 is a plan view showing a magneticsensor of the present embodiment. FIG. 21 is a plan view showing asecond resistor of the present embodiment.

The magnetic sensor 2 according to the present embodiment differs fromthat according to the first embodiment in the following ways. Themagnetic sensor 2 according to the present embodiment includes a firstresistor R111, a second resistor R112, a third resistor R121, and afourth resistor R122 instead of the first to fourth resistors R11, R12,R21, and R22 of the first embodiment. The first to fourth resistorsR111, R112, R121, and R122 are each configured to change in resistancewith the strength of the magnetic field component MFx (see FIG. 2). Thelayout of the first to fourth resistors R111, R112, R121, and R122 incircuit diagram and the layout of the first to fourth resistors R111,R112, R121, and R122 in physical configuration are the same as those ofthe first to fourth resistors R11, R12, R21, and R22 of the firstembodiment.

The first to fourth resistors R111, R112, R121, and R122 each include aplurality of MR elements 50. The first to fourth resistors R111, R112,R121, and R122 also each include a plurality of element groups. For theplurality of element groups, the first and third resistors R111 and R121each include eight element groups 31 to 38 having the configuration andpositional relationship shown in FIG. 6 in the first embodiment.

FIG. 21 is a plan view showing the second resistor R112. As shown inFIG. 21, the second resistor R112 includes eight element groups 131,132, 133, 134, 135, 136, 137, and 138. The element groups 131 to 138each have the same configuration as that of each of the element groups31 to 38. The element groups 131 to 134 have the same positionalrelationship as that of the element groups 31 to 34. The element groups135 to 138 have the same positional relationship as that of the elementgroups 35 to 38. In particular, in the second resistor R112, the elementgroups 135 to 138 are located along the X direction, anterior to theelement groups 131 to 134 in the Y direction.

The plurality of element groups in the fourth resistor R122 have thesame configuration and layout as those of the plurality of elementgroups in the second resistor R112. Specifically, the fourth resistorR122 includes eight element groups 131 to 138 having the configurationand positional relationship shown in FIG. 21.

In FIG. 20, the symbol L denotes an imaginary straight line parallel tothe X direction. In FIG. 20, the element groups 31 to 38 and 131 to 138are represented by rectangles divided in four sections like the elementgroups 31 to 38 in FIG. 6 and the element groups 131 to 138 in FIG. 21.In particular, in the present embodiment, as shown in FIG. 20, theelement groups 31 to 38 of the first resistor R111 and the elementgroups 131 to 138 of the second elements R112 are located at positionssymmetrical about the imaginary straight line L1. The plurality of MRelements 50 of the first resistor R111 and the plurality of MR elements50 of the second resistor R112 are located at positions symmetricalabout the imaginary straight line L. The element groups 31 to 38 of thethird resistor R121 and the element groups 131 to 138 of the fourthelements R122 are located at positions symmetrical about the imaginarystraight line L1. The plurality of MR elements 50 of the third resistorR121 and the plurality of MR elements 50 of the fourth resistor R122 arelocated at positions symmetrical about the imaginary straight line L.

As described above, in the present embodiment, a plurality of MRelements 50 included in two resistors connected in series are located atpositions symmetrical about the imaginary straight line L. According tothe present embodiment, the offsets of the first and second detectionsignals S1 and S2 when the magnetic sensor 2 or the magnetic fieldgenerator 3 is skewed can thus be reduced, compared to the magneticencoder of the third comparative example described in the firstembodiment.

The configuration, operation and effects of the present embodiment areotherwise the same as those of the first embodiment.

Third Embodiment

A third embodiment of the present invention will now be described withreference to FIGS. 22 and 23. FIG. 22 is a plan view showing a magneticsensor according to the present embodiment. FIG. 23 is a circuit diagramshowing the configuration of the magnetic sensor according to thepresent embodiment.

The magnetic sensor 102 according to the present embodiment includes afirst resistor R211, a second resistor R212, a third resistor R221, afourth resistor R222, a fifth resistor R231, a sixth resistor R232, aseventh resistor R241, and an eighth resistor R242 each configured tochange in resistance with the strength of the magnetic field componentMFx (see FIG. 2). The first to eighth resistors R211, R212, R221, R222,R231, R232, R241, and R242 each include a plurality of MR elements 50.The first to eighth resistors R211, R212, R221, R222, R231, R232, R241,and R242 each include eight element groups 31 to 38 having theconfiguration and positional relationship shown in FIG. 6 in the firstembodiment.

The magnetic sensor 102 further includes two power supply ports V11 andV12, two ground ports G11 and G12, a first output port E11, a secondoutput port E12, a third output port E21, a fourth output port E22, andtwo differential detectors 21 and 22. A voltage of predeterminedmagnitude is applied to each of the power supply ports V11 and V12. Theground ports G11 and G12 are grounded. The magnetic sensor 102 may bedriven by a constant voltage or driven by a constant current.

The differential detector 21 outputs a signal corresponding to apotential difference between the first and third output ports E11 andE21 as a first detection signal S11. The differential detector 22outputs a signal corresponding to a potential difference between thesecond and fourth output ports E12 and E22 as a second detection signalS12.

The differential detectors 21 and 22 are connected to the detectionvalue generation circuit 4 (see FIG. 4). In the present embodiment, thedetection value generation circuit 4 generates the detection value Vs onthe basis of the first and second detection signals S11 and S12. Atleast either the magnetic sensor 102 or the detection value generationcircuit 4 may be configured to be able to correct the amplitude, phase,and offset of each of the first and second detection signals S11 andS12. The method for generating the detection value Vs is the same asthat of the first embodiment except that the first and second detectionsignals S11 and S12 are used instead of the first and second detectionsignals S1 and S2.

As shown in FIG. 23, the first resistor R211 and the second resistorR212 are connected in series via a first connection point P11 connectedto the first output port E11. The third resistor R221 and the fourthresistor R222 are connected in series via a second connection point P12connected to the second output port E12. The fifth resistor R231 and thesixth resistor R232 are connected in series via a third connection pointP21 connected to the third output port E21. The seventh resistor R241and the eighth resistor R242 are connected in series via a fourthconnection point P22 connected to the fourth output port E22.

In circuit configuration, the first resistor R211 is located between thepower supply port V11 and the first connection point P11. An end (end inthe circuit diagram) of the first resistor R211 opposite to the firstconnection point P11 is connected to the power supply port V11.

In circuit configuration, the second resistor R212 is located betweenthe ground port G11 and the first connection point P11. An end (end inthe circuit diagram) of the second resistor R212 opposite to the firstconnection point P11 is connected to the ground port G11.

In circuit configuration, the third resistor R221 is located between thepower supply port V11 and the first connection point P12. An end (end inthe circuit diagram) of the third resistor R221 opposite to the secondconnection point P12 is connected to the power supply port V11.

In circuit configuration, the fourth resistor R222 is located betweenthe ground port G11 and the second connection point P12. An end (end inthe circuit diagram) of the fourth resistor R222 opposite to the secondconnection point P12 is connected to the ground port G11.

In circuit configuration, the fifth resistor R231 is located between thepower supply port V12 and the third connection point P21. An end (end inthe circuit diagram) of the fifth resistor R231 opposite to the thirdconnection point P21 is connected to the power supply port V12.

In circuit configuration, the sixth resistor R232 is located between theground port G12 and the third connection point P21. An end (end in thecircuit diagram) of the sixth resistor R232 opposite to the thirdconnection point P21 is connected to the ground port G12.

In circuit configuration, the seventh resistor R241 is located betweenthe power supply port V12 and the fourth connection point P22. An end(end in the circuit diagram) of the seventh resistor R241 opposite tothe fourth connection point P22 is connected to the power supply portV12.

In circuit configuration, the eighth resistor R242 is located betweenthe ground port G12 and the fourth connection point P22. An end (end inthe circuit diagram) of the eighth resistor R242 opposite to the fourthconnection point P22 is connected to the ground port G12.

As shown in FIG. 22, the magnetic sensor 102 further includes asubstrate 110, and two power supply terminals 111 and 112, two groundterminals 113 and 114, a first output terminal 115, a second outputterminal 116, a third output terminal 117, and a fourth output terminal118 that are located on the substrate 110. The power supply terminals111 and 112 constitute the power supply ports V11 and V12, respectively.The ground terminals 113 and 114 constitute the ground ports G11 andG12, respectively. The first to fourth output terminals 115, 116, 117,and 118 constitute the first to fourth output ports E11, E12, E21, andE22, respectively.

As shown in FIG. 22, the magnetic sensor 102 is divided between a firstportion 102A and a second portion 102B. In FIG. 22, the border betweenthe first and second portions 102A and 102B is shown by a dotted line.The second portion 102B is located in front of the first portion 102A inthe Y direction. The first portion 102A includes the first to fourthresistors R211, R212, R221, and R222, the power supply terminal 111, theground terminal 113, and the first and second output terminals 115 and116. The second portion 102B includes the fifth to eighth resistorsR231, R232, R241, and R242, the power supply terminal 112, the groundterminal 114, and the third and fourth output terminals 117 and 118.

The layout of the first to fourth resistors R211, R212, R221, and R222in the first portion 102A is the same as that of the first to fourthresistors R11, R12, R21, and R22 of the first embodiment. The layout ofthe fifth to eighth resistors R231, R232, R241, and R242 in the secondportion 102B is also the same as that of the first to fourth resistorsR11, R12, R21, and R22 of the first embodiment. In particular, in thepresent embodiment, the fifth and sixth resistors R231 and R232 arelocated at the same position as the first and second resistors R211 andR212 are in the X direction.

The configuration of the first to eighth resistors R211, R212, R221,R222, R231, R232, R241, and R242 described above makes a phasedifference of the ideal component of the second detection signal S12from the ideal component of the first detection signal S11 an odd numberof times ¼ of a predetermined signal period (the signal period of theideal component).

Each of the second, fourth, sixth, and eighth resistors R212, R222,R232, and R242 may include eight element groups 131 to 138 having theconfiguration and positional relationship shown in FIG. 21 instead ofthe eight element groups 31 to 38 having the configuration andpositional relationship shown in FIG. 6 in the first embodiment. Theconfiguration, operation and effects of the present embodiment areotherwise the same as those of the first or second embodiment.

The present invention is not limited to the foregoing embodiments, andvarious modifications may be made thereto. For example, the number andlayout of the MR elements 50 are not limited to the examples describedin the embodiments but may be freely set as long as the requirements setforth in the claims are satisfied.

The magnetic field generator 3 may be a rotary scale magnetized to aplurality of pairs of N and S poles along the direction of rotation. Therotary scale may be a ring-shaped magnet, or a magnetic medium, such asa magnetic tape, fixed to a ring or a disc.

In the third embodiment, the first portion 102A and the second portion102B may be separated. In the third embodiment, the resistors R211,R212, R231, and R232 may constitute a first Wheatstone bridge circuit,and the resistors R221, R222, R241, and R242 may constitute a secondWheatstone bridge circuit. In such a case, the first and secondWheatstone bridges may be driven by a constant voltage or driven by aconstant current.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. Thus, it is to beunderstood that, within the scope of the appended claims and equivalentsthereof, the invention may be practiced in other embodiments than theforegoing most preferable embodiments.

What is claimed is:
 1. A magnetic sensor for detecting a target magneticfield including a magnetic field component in a first direction parallelto an imaginary straight line, the magnetic sensor comprising: first tofourth resistors each configured to change in resistance with strengthof the magnetic field component; a power supply port to which a voltageof predetermined magnitude is applied; a ground port that is grounded; afirst output port; and a second output port, wherein the first resistorand the second resistor are located in a first region and connected inseries via a first connection point connected to the first output port,the third resistor and the fourth resistor are located in a secondregion and connected in series via a second connection point connectedto the second output port, at least a part of the second region beinglocated at a position different from the first region in the firstdirection, an end of the first resistor opposite to the first connectionpoint and an end of the third resistor opposite to the second connectionpoint are connected to the power supply port, an end of the secondresistor opposite to the first connection point and an end of the fourthresistor opposite to the second connection point are connected to theground port, and the first and second resistors are located between thethird and fourth resistors in a second direction orthogonal to the firstdirection.
 2. The magnetic sensor according to claim 1, wherein: acenter of gravity of the first resistor when viewed in a third directionorthogonal to the first and second directions and a center of gravity ofthe second resistor when viewed in the third direction are located atpositions symmetrical about the imaginary straight line; and a center ofgravity of the third resistor when viewed in the third direction and acenter of gravity of the fourth resistor when viewed in the thirddirection are located at positions symmetrical about the imaginarystraight line.
 3. The magnetic sensor according to claim 1, wherein acenter of gravity of a group including the first and third resistorswhen viewed in a third direction orthogonal to the first and seconddirections and a center of gravity of a group including the second andfourth resistors when viewed in the third direction are located atpositions symmetrical about the imaginary straight line.
 4. The magneticsensor according to claim 1, wherein: the first to fourth resistors eachinclude a plurality of magnetoresistive elements; and the plurality ofmagnetoresistive elements each include a magnetization pinned layerhaving a magnetization whose direction is fixed, a free layer having amagnetization whose direction is variable depending on the direction andthe strength of the magnetic field component, and a gap layer locatedbetween the magnetization pinned layer and the free layer.
 5. Themagnetic sensor according to claim 4, wherein: the direction of themagnetization of the magnetization pinned layer in each of the pluralityof magnetoresistive elements included in the first and third resistorsis a first magnetization direction; and the direction of themagnetization of the magnetization pinned layer in each of the pluralityof magnetoresistive elements included in the second and fourth resistorsis a second magnetization direction opposite to the first magnetizationdirection.
 6. The magnetic sensor according to claim 4, wherein: theplurality of magnetoresistive elements of the first resistor and theplurality of magnetoresistive elements of the second resistor arelocated at positions symmetrical about the imaginary straight line; andthe plurality of magnetoresistive elements of the third resistor and theplurality of magnetoresistive elements of the fourth resistor arelocated at positions symmetrical about the imaginary straight line. 7.The magnetic sensor according to claim 4, wherein each of the pluralityof magnetoresistive elements further includes a bias magnetic fieldgenerator that generates a bias magnetic field in a directionintersecting the first direction, the bias magnetic field being appliedto the free layer.
 8. The magnetic sensor according to claim 4, whereinthe free layer has magnetic shape anisotropy with a direction of an easyaxis of magnetization intersecting the first direction.
 9. The magneticsensor according to claim 4, wherein the gap layer is a tunnel barrierlayer.
 10. A magnetic encoder comprising: the magnetic sensor accordingto claim 1; and a magnetic field generator that generates the targetmagnetic field, wherein the magnetic sensor and the magnetic fieldgenerator are configured so that the strength of the magnetic fieldcomponent changes with a change in a position of the magnetic fieldgenerator relative to the magnetic sensor.
 11. The magnetic encoderaccording to claim 10, further comprising a detection value generationcircuit, wherein: the magnetic sensor generates a first detection signalhaving a correspondence with a potential at the first output port, andgenerates a second detection signal having a correspondence with apotential at the second output port; and the detection value generationcircuit generates a detection value having a correspondence with theposition of the magnetic field generator relative to the magnetic sensoron a basis of the first and second detection signals.
 12. The magneticencoder according to claim 11, wherein: the magnetic field generator isa magnetic scale including a plurality of pairs of N and S polesalternately arranged in a predetermined direction; the first and seconddetection signals each contain an ideal component varying periodicallyto trace an ideal sinusoidal curve, and an error component correspondingto a harmonic of the ideal component; and the first to fourth resistorsare configured so that the ideal component of the first detection signaland the ideal component of the second detection signal have respectivedifferent phases and the error components are reduced.
 13. A lensposition detection device for detecting a position of a lens whoseposition is variable, the lens position detection device comprising: themagnetic sensor according to claim 1; and a magnetic field generatorthat generates the target magnetic field, wherein the lens is configuredto be movable in the first direction, and the magnetic sensor and themagnetic field generator are configured so that the strength of themagnetic field component changes with a change in the position of thelens.
 14. The lens position detection device according to claim 13,further comprising a detection value generation circuit, wherein: themagnetic sensor generates a first detection signal having acorrespondence with a potential at the first output port, and generatesa second detection signal having a correspondence with a potential atthe second output port; and the detection value generation circuitgenerates a detection value having a correspondence with the position ofthe lens on a basis of the first and second detection signals.
 15. Thelens position detection device according to claim 14, wherein: themagnetic field generator is a magnetic scale including a plurality ofpairs of N and S poles alternately arranged in a predetermineddirection; the first and second detection signals each contain an idealcomponent varying periodically to trace an ideal sinusoidal curve, andan error component corresponding to a harmonic of the ideal component;and the first to fourth resistors are configured so that the idealcomponent of the first detection signal and the ideal component of thesecond detection signal have respective different phases and the errorcomponents are reduced.